Active suspension feeders, living in the top few centimetres of sediment. They are easily dislodged by storms and cockle beds can be washed away during winter gales. Commercially fished in areas such as Morecambe Bay, the Wash, Thames Estuary, Dee Estuary, Outer Hebrides and South Wales.

Seasonal Growth
Growth in Cerastoderma edule shows a marked seasonal pattern (Seed & Brown, 1977; Hancock & Franklin, 1972). In the Burry Inlet, Wales, shell growth commenced in May, continued through June until late August after which growth was negligible. Winter growth rates vary, e.g. negligible winter growth occurred for less than a month in the Menai Straits, Wales but for 158 days (between May -October) in Sorbotn, Norway although growth was more vigorous in young (first winter) than older specimens (Richardson et al. 1980). Adults may loose weight over winter (Hancock & Franklin, 1972; Newell & Bayne, 1980) probably due to lack of food. Mortality over winter was reported by several authors, e.g. Hancock & Urquhart (1964) report normal winter mortalities of 30 -90% in Burry Inlet, depending on size. After spawning the high food availability and reduced metabolic costs (compared with prior gametogenesis) allows Cerastoderma edule to synthesize carbohydrate reserves. The decline in body weight over winter and early spring is associated with the utilisation of lipid, protein and carbohydrate reserves (Newell & Bayne, 1980).

Growth banding
Reduced or negligible winter growth, together with disturbance results in clearly distinguishable external banding. Internal bands are laid down at semi-diurnal intervals related to the tidal cycle. Winter growth and internal bands have been used to age cockles, examine the past history of populations, population dynamics and monitoring (Orton, 1926; Richardson et al. 1979; Richardson et al., 1980; Jones & Baxter, 1987a).

Parasitism Boyden (1972) reported castration of 13% of the population of Cerastoderma edule in the River Couch estuary due to infection with larval digenetic trematodes. Jonsson & Andre (1992) suggested that mass mortality of Cerastoderma edule occurring on the west coast of Sweden in the summer of 1991 was due to infestation by the larvae of the digenean trematode Cercaria cerastodermae I. Cercaria cerastodermae I has been recorded on British shores but was considered rare. The brucephalid cercariae, Cercaria fulbrighti primarily occupies digestive gland, foot and gonads. The parasitic copepod Paranthessius rostatus was reported in the mantle cavity of cockles around the British Isles (Atkins, 1934) and the Dutch Wadden Sea (sometimes 10s of parasites per individual) (Kristensen, 1958). The rhabdocele Paravortex cardiiand Paravortex karlings have also been reported in Cerastoderma edule in the British Isles (Pike & Burt, 1981; Atkins, 1934).

Boyden & Russell (1972) compared the habitat preferences of Cerastoderma edule and Cerastoderma glaucum. They concluded that Cerastoderma edule was excluded from hypo- or hyper-saline waters by insufficient tidal flow rather than salinity itself, and that Cerastoderma edule was unable to colonize still water conditions. Brock (1979) found Cerastoderma edule in Danish fjords with little tidal range and suggested that food availability was more important. However, Cerastoderma edule and Cerastoderma glaucum may be found together (sympatric), where stable sediments and good food availability occur e.g. Zostera sp. covered silt banks (Boyden & Russell, 1972; Brock, 1979).

PredationPredation has been show to influence recruitment and population dynamics in Cerastoderma edule. (Sanchez-Salazar et al., 1987a; Masski & Guillou, 1999;. Sanchez-Salazar et al. (1987a) reported that low shore cockles had high mortalities when small which decreased with size due to predation by shore crab (Carcinus maenas) in the summer months that preferred cockles <15mm in length. Higher on the shore cockle mortality was moderately in the first year (47%) but increased with size, due to predation by oystercatchers (Haematopus ostralegus) in the winter months, which prefer cockles of at least 20mm in length. As a result, the lower shore populations studied were composed of spat and fewer large individuals whereas higher shore populations contained smaller cockles.

Cockles are also preyed on by the shrimp and flatfish, e.g. in Sweden Crangon crangon was a dominant predator of cockles <2mm and cockles were the dominant food for the flounder Platichthys flesus (Möller & Rosenberg, 1983). Möller & Rosenberg, (1983) noted that predators removed a significant proportion of bivalve production in years of normal recruitment, less so in years of good recruitment.

Longevity and sexual maturityCerastoderma edule may live for up to 9 years or more in some habitats but 2 -4 years is normal. The sex ratio was reported to be 40% males to 60% females (Fretter & Graham, 1964). Adults first mature and spawn in their second summer, at about 18 months old and 15-20 mm in length, however, large cockles (>15 mm) may mature in their first year suggesting that size and maturity are linked (Orton, 1926; Hancock & Franklin, 1972; Seed & Brown, 1977).Reproductive cycle Gametogenesis is initiated in winter (October to March) but increases rapidly in spring (February -April) (Newell & Bayne, 1980) and the majority of the population are ripe by mid-summer (Seed & Brown, 1977). Most adults spawn in a short peak period over summer with remaining adults spawning over a protracted period, resulting in a short (ca. 3 month) period of peak settlement followed by generally declining numbers of recruits (Hancock, 1967; Seed & Brown, 1977). Spawning generally occurs between March - August in the UK followed by peak spatfall between May and September, however the exact dates vary between sites in the UK and Europe (Seed & Brown, 1977; Newell & Bayne, 1980). Boyden (1971) suggested that warming of water in spring to 13 °C or above was required to induce spawning, however Ducrotoy et al. (1991) suggested that a sudden temperature rise (rather than an absolute level) was probably required to initiate spawning. An occasional late peak in settlement may occur e.g. on the Llanrhidian Sands, Hancock (1967) reported an additional settlement peak in August -September after the main peak in May -July.Development Fertilization is external. Males may release about 15 million sperm/sec and females were reported to release about 1900 eggs/sec. Gamete viability is short and André & Lindegarth (1995) found that fertilization was reduced to 50% in 2 hours and that no fertilization was observed after 4 -8 hrs. André & Lindegarth (1995) noted that fertilization efficiency was dependant on sperm concentration so that at high water flow rates fertilisation was only likely between close individuals. However, this may be compensated for by high population densities and synchronous spawning of a large proportion of the population. Eggs (50-60µm) develop into a trochophore stage within the egg membrane and then into a typical bivalve veliger at ca. 80µm, the D -larvae (so called due to the D -shaped shell) after about 3 -4 days the foot develops and the veliger metamorphoses into a juvenile cockle (pediveliger) at ca. 270µm after about 3 -5 weeks (Lebour, 1938; Creek, 1960). The juveniles reach ca. 600-700µm after about 3 weeks, and by 3 months are ca. 0.75-1.5 mm long (Creek, 1960).Recruitment Settlement and subsequent recruitment has a significant impact on the dynamics of Cerastoderma edule populations, in many but not all circumstances (Olaffsson et al., 1994). Settlement and recruitment is sporadic and varies with geographic location, year, season, reproductive condition of the adults and climatic variation. Factors reported to affect recruitment follow.

Geographical location (Ducrotoy et al. 1991; Olaffsson et al., 1994).

Annual variation in climate. Ducrotoy et al. (1991) reported the variation in annual recruitment between years for several sites in Europe, and noted a correlation between good recruitment and a previous severe winter (presumably due to high adult mortality, reduced population density of adults and reduced numbers of infaunal predators), in many but not all cases.

Good recruitment was also observed after heavy storm surges reduced the adult population (Ducrotoy et al. 1991).

Post-settlement erosion and surface sediment erosion by currents and storms. Juveniles may be transported by currents until 2mm in size and high densities of juveniles may be swept away by winter storms resulting in subsequent patterns of adult distribution (Olaffsson et al., 1994).

Adult suspension feeders, including adult cockles, may reduce settlement by ingestion of settling larvae and juveniles or smothering by sediment displaced in burrowing and feeding (Montaudouin & Bachelet, 1996). Therefore, recruitment may be dependant on adult population density (André et al.,1993). André et al. (1993) observed that adults inhaled 75% of larvae at 380 adults/m², which were also ingested. However, Montaudouin & Bachelet, (1996) noted that adults that inhaled juveniles, rejected them and closed their siphons but that rejected juveniles usually died.

Guillou & Tartu (194) noted that spat also suffered from mortality in their first year in the spring following their settlement, even through food was available, probably due to exhausted energy reserves (after winter) and spring predation from shore crabs.